Integrated circuits typically begin fabrication as a die on a flat, circular substrate or wafer. The die comprises a rectangular portion of the wafer surface and is also known as a chip, circuit, or the like. Each wafer usually is segmented by scribe or saw lines into multiple dies, which typically form essentially identical rectangular circuit patterns. Some dies may be engineering or test dies. Other dies may be edge dies where the wafer does not permit the formation of a complete die along the edge of the wafer. On many wafers, there is a kerf area or area between the dies. The size of the kerf area varies as the number and arrangement of the dies on the wafer varies. When fabrication is completed, the wafer is cut along the kerf area to separate the dies for use in IC devices.
Dies are tested after fabrication to determine whether a suitable IC has been manufactured. The dies may be individually tested after separation of the wafer. The dies also may be serially tested before separation of the wafer. Die testing usually involves the use of mechanical probes from a testing device. The mechanical probes engage test pads or pins on the die. Once engaged, the testing device applies input signals or voltages to the die and then receives output signals or voltages from the die.
Generally, the testing device needs to have the same number of data tester channels as the number of data pins on the die. If a die has eight data pins, then eight data tester channels usually are connected to the eight test pins on the die for reading and writing data. In this type of testing system, the maximum number of dies that can be tested at the same time is equal to the total number of data tester channels divided by the number of data pins per die.
In other testing systems, dies are connected in parallel on the wafer. Each die has separate data pins for testing different sections or areas of the die. Data pins for similar sections or areas of each die are interconnected via a bus or other routing mechanism with a wafer test pad. Similar data pins on each die perform the same test on each die or test the same portion of each die. During testing, a data tester channel is connected to each wafer test pad for reading and writing data to the same section or area of each die. While multiple dies are tested in parallel, the testing device can test only a limited number of dies. The number of dies tested at the same time is limited by the number of data pins on each die, and hence the number of data tester channels required per die. Many testing devices have a limited number of available channels for testing.